The present invention generally relates to molding compositions and to the use of particular wax esters in reducing the force needed to release a molded thermoplastic resin from an injection mold or the like. More particularly, the thermoplastic molding composition includes a thermoplastic acrylonitrile-butadiene-styrene resin and a cetyl ester mold release agent, as well as the use of a cetyl ester mold release agent in a method for reducing the mold release force required for removing a molded thermoplastic acrylonitrile-butadiene-styrene polymer from an injection molding unit. By proceeding in accordance with this invention, the mold release force is reduced by approximately 10 percent or more, such force reduction being accomplished without needing to add free carboxylic acid to the molding resin composition, the invention avoids any significant deterioration of the mechanical properties of the molded acrylonitrile-butadiene-styrene, and same does not cause any change in the appearance thereof.
Lubricants are conventionally employed in the processing of generally rigid plastic materials such as acrylonitrile-butadiene-styrene resins or polymers in order to improve the processability of the resin or polymer. It has been found that incorporating such lubricants into these generally rigid molding resins or polymers results in an improvement in the mold release properties of these resinous or polymeric products when they are injection molded. Known lubricants, especially in connection with the molding of polycarbonate molding compositions, include various carboxylic acids and esters. Mold release enhancement has been well developed, and numerous lubricant components are available and suitable for reducing the mold release force required for polycarbonate molding compositions, as well as other resin and polymer molding compositions.
When the resin or polymer of the injection molding composition is an acrylonitrile-butadiene-styrene thermoplastic material, problems are frequently encountered due to the force required when removing the molded part from the injection molding unit. While various lubricants have been proposed and utilized in an effort to reduce the mold release force required in this regard, the incorporation of such lubricants brings with it the concern that the molded acrylonitrile-butadiene-styrene products will exhibit significant losses with respect to the mechanical properties of the molded resin or polymer, as well as an undesirable change in appearance of the molded part made from a lubricated composition when compared with one made from an unlubricated one. Also, many lubricating-type additives are not especially effective in enhancing the ease of mold release of acrylonitrile-butadiene-styrene parts to any substantial extent.
Some lubricants that are suitable for enhancing the mold release properties of rigid resins or polymers such as polycarbonate are not particularly suitable or useful in achieving mold release enhancement properties when those same lubricants are used in conjunction with the molding of acrylonitrile-butadiene-styrene resins or polymers. Other lubricants may cause serious deterioration of mechanical properties and/or of the physical appearance of molded acrylonitrile-butadiene-styrene molding compositions, thereby making them less than satisfactory despite their effectiveness in reducing the force needed to push the shaped plastic piece out of the mold.
Accordingly, there is a need for a mold release composition and method for improving the mold release properties of acrylonitrile-butadiene-styrene injection molding compositions while at the same time minimizing or substantially eliminating any deterioration in the physical properties of the molded part and without detracting from or otherwise changing the appearance of the molded part in comparison to the physical properties and appearance of acrylonitrile-butadiene-styrene parts that are molded without the aid of lubricants or mold release agents. It would also be desirable to provide a mold release enhancement method and composition that is not complex and that is realized by the addition of but a single component to the acrylonitrile-butadiene-styrene component.
By the present invention, a thermoplastic molding composition is provided which exhibits mold release properties that include a significant reduction in the force required to remove parts molded therefrom from injection molding devices, which thermoplastic molding composition does not exhibit a significant deterioration of physical properties or change in appearance from the physical properties and appearance of acrylonitrile-butadiene-styrene resins that are not modified with a lubricant or mold release agent or the like. Included in accordance with the present invention is the addition of a cetyl ester component to an acrylonitrile-butadiene-styrene resin in mold release effective amounts and molding same, typically in accordance with injection molding techniques, followed by ejecting same from the mold with reduced mold release forces in order to provide a finished acrylonitrile-butadiene-styrene part that has substantially the same physical properties and appearance as substantially unmodified acrylonitrile-butadiene-styrene polymer parts.
It is accordingly a general object of the present invention to provide an improved thermoplastic molding composition and method of enhancing the mold release attributes of the resin.
Another object of the present invention is to provide an improved thermoplastic acrylonitrile-butadiene-styrene molding composition that includes a mold release agent which significantly reduces mold release forces without substantially affecting the physical properties of the molded product.
Another object of this invention is to provide a method for improving the mold release properties of an acrylonitrile-butadiene-styrene product without seriously deteriorating the physical properties of the molded product and without perceptibly modifying the appearance of the molded product.
Another object of this invention is to utilize certain wax esters as lubricant components in an acrylonitrile-butadiene-styrene molding composition and method.
Another object of the present invention is to provide an improved molding composition and method for acrylonitrile-butadiene-styrene molding which does not require and which can preclude the use of free carboxylic acids within the molding composition.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.